The present invention relates to the purification of gases in general, and more particularly to a method of purifying combustion product gases which are contaminated with dust and noxious gases.
There are already known various methods of purifying discharge gases which are contaminated with dust and noxious gases, especially combustion product gases discharged from fossil fuel burning plants, which carry entrained dust including alkali and/or alkaline earth compounds as they leave the combustion chamber and/or as a result of the addition thereto of alkali or alkaline earth compounds, especially at least one of Ca(OH).sub.2, CaCO.sub.3, NaHCO.sub.3, Na.sub.2 SO.sub.4, NaOH, hydroxides, oxides, carbonates, sulfates, and bicarbonates, after the performance of a partial desulfurization. So, for instance, it is known to utilize lime for the desulfurization of the combustion product gases, and to blow this lime into the combustion chamber of the steam-generating boiler, as well as to separate the corresponding reaction product from the combustion product gases. In this single-stage process, there is generally obtained a desulfurization degree of 50%, which is too low to satisfy the current legal requirements. It is further known to arrange for a second sorbent addition (for instance Ca(OH).sub.2 and/or NaHCO.sub.3) into the already partially cooled off combustion product gases, and in this manner to achieve a further desulfurization. However, even in this process the desulfurization degree is limited to about 80%, and no removal of NO.sub.x takes place. A separate arrangement, often provided with catalysts, is then provided for the removal of NO.sub.x.